This invention relates to a surgical device for inactivating venous valve cusps for use in the preparation of a vein for in situ vein bypass.
Autogenous venous bypass is a popular method for the surgical treatment of femoropopliteal arterial obstruction. Generally, the procedure involves the use of the long saphenous vein, a vein passing up the leg from the ankle to the groin, to form a conduit around a blocked artery. To use this easily accessible vein as a bypass conduit, it is first necessary to overcome the barrier imposed by the vein valves. In particular, the saphenous vein is intersected by three to seven valves. The valves allow blood to pass upwards toward the heart and prevent blood from flowing in reverse while one is in an upright position. Deactivation of the venous valves is required to permit use of the vein as an arterial bypass conduit.
Deactivation of the venous valves was first accomplished by severing and removing the saphenous vein from the body, reversing the vein, and rejoining the vein to an artery at points above and below the area of arterial blockage. Arterial blood flows past the valves in an unobstructed manner because the valves are redirected by reversing the vein. However, there are many potential surgical problems encountered with reversed-vein bypassing procedures, including twisting and compressing of the body of the vein during the vein removal and reversal process. There are also problems in anastomosising or grafting the smaller diameter of the reversed vein to the larger diameter, thicker portion of the artery, and vice versa. Moreover, the preservation of the highly sensitive endothelial layer of the vein conduit is of utmost importance to successful bypass results and requires careful attention and surgical procedures to ensure such preservation.
Alternative in situ vein bypass procedures were developed in response to the problems encountered with reversed-vein bypass methodology. In situ vein bypass refers to the use of a vein as it lies anatomically within the body, i.e., without removal and reversal of the vein. There are many advantages associated with the in situ method. For example, the potential for twisting of the vein in situ is greatly reduced. Because the vein is not reversed, the larger end of the vein is attached to the larger portion of the femoral artery and the smaller distal end of the vein is attached to the smaller distal portion of the artery. The anastomosis is therefore easier to construct and, because the vein is tapered from entrance to outlet, the resultant conduit is hemodynamically sound, resulting in improved blood flow. Moreover, by utilizing the vein in situ, minimal vein dissection occurs and the endothelial lining of the vein can be better preserved.
The most critical step in the in situ procedure is producing valve incompetence within the vein. To date, the only certain way of inactivating the valve cusps or leaflet pairs is by complete excision of the valve cusps. Existing methods for accomplishing valve excision involve pulling or pushing a valve cutter or valvulotome down through the inside of a vein to excise vein leaflets. Before the cutting device is drawn through the vein, the vein is distended or pressurized with fluid to close the valves. This can be accomplished by grafting the top of the vein to the artery so that pressurized arterial blood passes into the vein. Alternatively, a saline solution can be pumped through a canulla into the top of the vein lumen as the pressurizing fluid. The blood or saline descends through and distends the vein, causing the first pair of valve leaflets or cusps to stretch across the vein and to close tightly. The valve cutter is then pulled through the tightly closed valve leaflets, thereby destroying or excising the venous valve leaflets. The pressurized fluid passes through the destroyed valve, causing the next valve to close. This pressurization and cutting procedure is carried out in succession for each valve leaflet pair. When all the valves are destroyed, the vein becomes a workable arterial bypass conduit. This procedure and various prior art cutting devices are described in Samuels, Plested, Haberfeld, Cincotti, and Brown, The American Surgeon, 34, 2, February, 1968, 122-130 and Leather, Shah, Corsin and Carmody, Journal of Vascular Surgery, 1, 1, 113-123, January, 1984. These prior devices, however, are quite difficult to manipulate and control and often cause significant trauma and damage to the vein.
Other, more recent devices for disabling valve cusps are known. For example, U.S. Pat. No. 4,655,217, describes a valve cutting device wherein retractable wire hooks are positioned within a flexible guide tube. When the wire hooks are moved from their retracted position within the tube to an extended position toward the vein wall, valve cusps are entrapped and disabled upon pulling the hooks down through the valve cusps.
The valve cutter disclosed in U.S. Pat. No. 4,493,321 utilizes a reversed arrowhead design for cutting valve leaflets. The device includes a rounded leading device to prevent damage to the vein wall, a straight cutting blade positioned between two protective supports, and a flexible rod connecting the leader to the cutting blade. The use of this device requires continuous controlled orientation of the straight cutting blade within the vein to prevent the cutting blade from catching and tearing the orifice wall of a venous branch and to ensure efficient engagement and incision of both valve leaflets. The device is useful only for those portions of the saphenous vein above the knee. The removal of valves in the smaller distal portions of the vein extending below the knee requires a different cutter device.
Thus, there is a need for an improved, self-centering, self-orienting, valvulotome.
Accordingly, an object of this invention is to provide a new and improved valvulotome.
A more particular object is to provide a valve cutter that does not require orientation within the vein to ensure contact with and intersection of the apposed valve leaflet pair.
Another object is to provide a cutting member that will engage leaflets without slipping away from the leaflet during excision.
Yet another object of this invention is to provide a valvulotome having a cutting edge that will only contact and cut valve leaflets and will not impinge on the wall of the vein or catch in the openings of vein branches.
In keeping with one aspect of this invention, a circular cutting head is affixed to a cable or wire and is, preferably, preceded by a dilating segment also affixed to the wire. The dilating segment straightens out the vein and centers the cutting head within the vein so that the cutting head does not impinge on the vein walls or enter a venous branch. The circular cutting edge permits engagement of the valve cusps without separate, continuous surgical orientation of the cutting device within the vein. A serrated or toothed cutting edge further promotes engagement of the valve leaflets and also helps to prevent slippage of the valve leaflet pairs. The serrated cutting edge is tapered inward to prevent trauma to or tearing of the venous wall.
In use, the cutting head, centering device, and cable are inserted into the saphenous vein at the distal anastomotic site or through a tributary vein. The cutting head and dilating or centering segment are inserted up through the vein and successive valve cusps to the proximal anastomatic site. The vein is pressurized with arterial blood or other fluid to close the first valve cusp. The cutting device is then drawn down through the tightly closed valve leaflet pairs. As the device is drawn, the lips of the valve leaflets are guided into the sharpened arcuate grooves of the toothed cutting edge. A slight pull on the device cuts the valve leaflets. This procedure is repeated as the valvulotome is withdrawn down the length of the vein until all valves have been rendered incompetent. Thus, the vein is prepared in situ for use as an arterial bypass conduit.